For instance, you have to pay Datadog per host you install the agent on. In addition to the per host cost, you have to pay per container you run on that host (past a very small baseline per host), and the per contain cost turns out to be nearly as high as the per host cost if you have reasonable density. Why am I paying Datadog per container I run? Aside from a not particularly useful dashboard, why does a process namespace and some cgroup metrics nearly double my bill? They are literally just processes on a server. Because Datadog wants you to run more hosts, so you install more agents.
Every feature they add also seems to be charged separately, but is not behind any sort of feature gate. This means new features just show up for my developers, and they have no clue if it costs money to use them. I can't just disable or cap, for example, their custom metrics per user, per project, or at all. So when my developers see a useful feature and start using it, all of a sudden I have an extra $10k on my monthly bill. Even more fun are features that show up and are initially free but then start charging.
This is such a pain that we've had to tell dev teams not to use Datadog features outside of a curate list. Every product has some rough edges, but with Datadog the patterns are all setup such that you end up paying them thousands of extra dollars. Again, great product, but not a business I would be interested in associating with again given the choice.